1/* Copyright 2022 The TensorFlow Authors. All Rights Reserved.
2
3Licensed under the Apache License, Version 2.0 (the "License");
4you may not use this file except in compliance with the License.
5You may obtain a copy of the License at
6
7 http://www.apache.org/licenses/LICENSE-2.0
8
9Unless required by applicable law or agreed to in writing, software
10distributed under the License is distributed on an "AS IS" BASIS,
11WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12See the License for the specific language governing permissions and
13limitations under the License.
14==============================================================================*/
15
16#ifndef TENSORFLOW_CORE_KERNELS_RANDOM_INDEX_SHUFFLE_H_
17#define TENSORFLOW_CORE_KERNELS_RANDOM_INDEX_SHUFFLE_H_
18
19#include <array>
20
21#include "tensorflow/core/platform/types.h"
22
23namespace tensorflow {
24namespace random {
25
26// Returns the position of `index` in a permutation of [0, ..., max_index].
27//
28// Index must be number in [0, ..., max_index].
29// Key is the random key for the permutation.
30// The returned index will also be in [0, ..., max_index]. For a fixed `key`
31// and `max_index` the all possible `index` values and the returned values
32// form a bijection.
33// Rounds must be a positive even integer >= 4. Larger values increase improve
34// 'randomness' of permutations for small `max_index` values. The time to
35// compute the result scales linear with the number of rounds. We recommend 8
36// rounds for a good treat off.
37//
38// For more details on the algorithm see the top of the cc file.
39uint64_t index_shuffle(const uint64_t index, const std::array<uint32_t, 3>& key,
40 const uint64_t max_index, const int32_t rounds);
41
42} // namespace random
43} // namespace tensorflow
44
45#endif // TENSORFLOW_CORE_KERNELS_RANDOM_INDEX_SHUFFLE_H_
46